On the random neighbor Olami-Feder-Christensen slip-stick model

We reconsider the treatment of Lise and Jensen (Phys. Rev. Lett. 76, 2326 (1996)) on the random neighbor Olami-Feder-Christensen stik-slip model, and examine the strong dependence of the results on the approximations used for the distribution of states p(E).Comment: 6pages, 3 figures. To be published in PRE as a brief repor

Steady-State Analysis of a Directional Square Lattice Band-Edge Photonic Crystal Lasers

The original square-lattice band-edge structure emitted light in different directions. In a recent paper, we have improved the directivity of these structures by using a honeycomb photonic crystal to shield the original structure. This has improved the performance of such devices, in such a way that light can be coupled directionally to a large waveguide. In this paper, we present a steady-state analysis of the performance of this directive device and study the amount of power which can be coupled into the waveguide, analyzing its performance as an in-plane emitter and the limitations caused by vertical losses

Uma interpretação sobre a evolução da produtividade industrial no Brasil nos anos noventa e as "leis" de Kaldor [An interpretation of industrial productivity evolution in Brazil in the nineties and the Kaldor 'laws']

The aim of this paper is to recover Kaldor´s propositions to shed some light on the recent debate about industrial productivity in Brazil. Nowadays, it is a well-disseminated idea that the opening of the economy has contributed to the increased industrial productivity in the nineties. However, theoretical arguments have emphasized supply sources as the main cause of such an increased productivity. Following the Keynesian tradition, Kaldor emphasizes the importance of the aggregate demand components to explain productivity growth. In conclusion, we call attention to the fact that sustainability of productivity growth depends basically on the factors working on the aggregate demand side.industrial productivity, industrial growth, structural change

Incidencia de la jornada escolar en los procesos de socializácion infantil

El artículo, derivado de la tesis doctoral realizada por la autora, sitúa elpunto de análisis en la percepción del tiempo social en general, y particularmente el escolar, como una realidad materializada en significados diversos para las niñas y niños, generadores de tensiones y conflictos en los procesos de socialización infantil. La vida cotidiana de la infancia en sus contextos familiar, extrafamiliar y escolar, está fuertemente mediatizada por las demandas y presiones del tiempo escolar que preside y organiza la vida de los pequeños y sus familias. El artículo analiza esta incidencia tomando como variable fundamental la modalidad de jornada lectiva, unidad temporal que ha usurpado el debate sobre la globalidad de los tiempos escolares y educativos que es, no sólo deseable, sino urgente en el contexto español. En el estudio se aportan los resultados obtenidos en la investigación realizada con alumnado gallego de Educación Primaria, alrededor de las siguientes cuestiones: planificación, administración y gestión del tiempo; percepción de su transcurrir y valoración de su disponibilidad y uso en los ámbitos familiar, escolar y extraescolar. La variable modalidad de jornada escolar (sesión única matinal/sesión partida mañana y tarde) se ha tomado como principal referencia en el análisis

Concentração industrial e produtividade do trabalho na indústria de transformação nos anos 90: evidências empíricas

This paper discusses the evolution of industrial concentration from 1985 to 1998. In the first part we associate this discussion to the degree of technological intensity in industry. To conduct this investigation, we had to make comparable the industrial classification in 1985, 1994 and 1998. After that, we classified all the industrialsectors according to the intensity in technology. In the second and third parts of this paper we discuss the association of employment and technological intensity and productivity and industrial concentration. We add to this last discussion an investigation about concentration and the participation of foreign capital in industry.industrial concentration, productivity, technology

Symmetry and Control of Spin-Scattering Processes in Two-Dimensional Transition Metal Dichalcogenides

Transition metal dichalcogenides (TMDs) combine interesting optical and spintronic properties in an atomically-thin material, where the light polarization can be used to control the spin and valley degrees-of-freedom for the development of novel opto-spintronic devices. These promising properties emerge due to their large spin-orbit coupling in combination with their crystal symmetries. Here, we provide simple symmetry arguments in a group-theory approach to unveil the symmetry-allowed spin scattering mechanisms, and indicate how one can use these concepts towards an external control of the spin lifetime. We perform this analysis for both monolayer (inversion asymmetric) and bilayer (inversion symmetric) crystals, indicating the different mechanisms that play a role in these systems. We show that, in monolayer TMDs, electrons and holes transform fundamentally differently -- leading to distinct spin-scattering processes. We find that one of the electronic states in the conduction band is partially protected by time-reversal symmetry, indicating a longer spin lifetime for that state. In bilayer and bulk TMDs, a hidden spin-polarization can exist within each layer despite the presence of global inversion symmetry. We show that this feature enables control of the interlayer spin-flipping scattering processes via an out-of-plane electric field, providing a mechanism for electrical control of the spin lifetime.Comment: 9 pages, 3 figure

Identification and tunable optical coherent control of transition-metal spins in silicon carbide

Color centers in wide-bandgap semiconductors are attractive systems for quantum technologies since they can combine long-coherent electronic spin and bright optical properties. Several suitable centers have been identified, most famously the nitrogen-vacancy defect in diamond. However, integration in communication technology is hindered by the fact that their optical transitions lie outside telecom wavelength bands. Several transition-metal impurities in silicon carbide do emit at and near telecom wavelengths, but knowledge about their spin and optical properties is incomplete. We present all-optical identification and coherent control of molybdenum-impurity spins in silicon carbide with transitions at near-infrared wavelengths. Our results identify spin $S=1/2$ for both the electronic ground and excited state, with highly anisotropic spin properties that we apply for implementing optical control of ground-state spin coherence. Our results show optical lifetimes of $\sim$60 ns and inhomogeneous spin dephasing times of $\sim$0.3 $\mu$s, establishing relevance for quantum spin-photon interfacing.Comment: Updated version with minor correction, full Supplementary Information include

Heterogeneidade intra-setorial da produtividade do trabalho na indústria brasileira nos anos 90

O objetivo deste trabalho é analisar os diferenciais dos níveis de produtividade do trabalho das empresas dentro dos grupos de atividade de três dígitos da Classificação Nacional de Atividade Econômica. Para realizar esta pesquisa, utilizamos informação de microdado das Pesquisas Industriais Anuais de 1996 e 1999 e do Censo Industrial de 1985. Constatamos que a distribuição das empresas segundo seus níveis de produtividade é muito concentrada em níveis muito baixos, mesmo em setores de alta intensidade tecnológica. Este resultado demonstra fato pouco destacado em estudos sobre a estrutura industrial brasileira, que é a elevada assimetria na distribuição das empresas dentro dos grupos de atividade. Do ponto de vista dos diferenciais de produtividade, setores de menor intensidade tecnológica apresentaram maior dispersão em termos relativos e absolutos. Os diferenciais de produtividade, de uma maneira geral, diminuíram de 1985 a 1996 e voltaram a aumentar de 1996 a 1999.

A indústria brasileira em 2004 e as teses sobre a sustentabilidade da retomada do crescimento

O objetivo deste trabalho é avaliar o desempenho da indústria em 2004, discutindo interpretações sobre a sustentabilidade do crescimento. Destaque é dado a argumentos que apontam o fraco dinamismo do mercado interno como evidência da não-sustentabilidade do crescimento e a argumentos que identificam o acelerado crescimento como uma ameaça à estabilidade de preços. Os desempenhos da produção industrial e da produtividade em 2004 são debatidos na parte final do texto